In general, light skin can become darker upon exposure to sunlight, which is the primary source of ultraviolet (UV) radiation in our daily life. Upon UV exposure, reactive oxygen species (ROS) and highly volatile free radicals are provoked. Consequently, our skin gets darkened since melanin-producing cells, or melanocytes, located in the skin's epidermis are prone to produce more melanin in order to minimize the indirect damages of body cells [Sklar L R, Almutawa F, Lim H W, Hamzavi I. Effects of ultraviolet radiation, visible light, and infrared radiation on erythema and pigmentation: a review. Photochemical & Photobiological Sciences 2013; 12:54-64]. In other words, the elevation of melanin production is actually a defense mechanism against UV radiation; however, the accumulation of melanin may result in deleterious biological effects, including abnormal pigmentation, skin darkening as well as aesthetic problems, e.g. freckles or chloasmata [Mishima Y, Imokawa G. Selective aberration and pigment loss in melanosomes of malignant melanoma cells in vitro by glycosylation inhibitors: premelanosomes as glycoprotein. Journal of Investigative Dermatology 1983; 81: 106-114]. In this regard, the formation of ROS and free radicals plays a pivotal mechanism leading to skin-darkening and skin-aging. Scavenging of ROS and free radicals can definitely protect skin cells from the oxidative damages. Currently, topical antioxidants, e.g. vitamin A, vitamin C, vitamin E, ascorbic acid (AC), butylated hydroxyanisole (BHA) and/or their derivatives, have been widely used in over-the-counter skincare products. However, these products are not effective skin-protection agents possessing both depigmentation and antioxidant properties. To this end, their effectiveness on skin protection is highly limited and restrained. There is a conception in the general public that dark and dull skin makes people look old, depressing and disfigured; therefore, people, especially in oriental countries, are eager to maintain a fair complexion and a pleasing appearance of their integumentary system.
In fact, melanin refers to a group of endogenous pigments that give multitude of skin colors, i.e. from the basic skin tone to freckles, birth marks, age spots, also in eyes and hair. In the human body, melanins are produced by melanocytes and classified into three major types: eumelanin, pheomelanin and neuromelanin. They differ in chemical structures and physical properties, and thus they are elicited upon different biological responses against external stimuli. Eumelanin and pheomelanin are the two types of melanin that can be found in the skin. Eumelanin provides primarily dark brown to black colors whereas pheomelanin produces reddish colors [Maresca V, Flori E, Picardo M. Skin phototype: a new perspective. Pigment Cell & Melanoma Research 2015; 28:378-389]. In melanogenesis, tyrosinase is the major rate-limiting enzyme for regulating melanin production in epidermal melanocytes whereas tyrosinase-related proteins (TRPs) are melanogenic enzymes that control the proportion of carboxylated subunits in melanin biopolymers. When exposed to sunlight, melanin deposition is accelerated as more alpha-melanocyte-stimulating hormone (α-MSH) is released from melanocytes. In addition to the overt skin darkening, such acceleration is indeed a defense mechanism against the UV-induced generation of ROS and/or free radicals, which consequently causes most of the wrinkles, freckles, rashes and age spots on the face. Collectively, the harmful effects of constant or excessive sunlight or UV exposure include skin aging, skin damage and even skin cancer. The present invention provides a composition that efficiently attenuates the biosynthesis of melanin as well as oxidative substances. By any means of mechanism, the present invention is able to restrain melanin accumulation and/or oxidative damage in the skin, hence skin protection can be achieved.
The composition of present invention comprises stilbenoids and/or extracts obtained from plants of the genus Dendrobium (Orchidaceae family, commonly called “Shi Hu”), particularly from the species D. officinale and D. nobile. The said stilbenoids, explicitly trans-resveratrol and dihydro-resveratrol, and extracts can be formulated into a cosmetic blend of skin-protection, skin-whitening and/or anti-skin aging products for human skin as they are found to attenuate the generation of ROS and oxidative free radicals, and/or reduce cellular melanin content in melanocytes. The reduction of melanin formation may be associated with an inhibition of the activity of pigment-producing enzymes, namely tyrosinase, TRP-1 and TRP2.